1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying a sheet.
2. Description of the Related Art
In recent years, a sheet conveying apparatus in which sheets discharged from an image forming apparatus such as a printer or a copying machine are sorted into sheet groups, and the sorted sheets are each shifted in a width direction set for the corresponding sheet group, and are sorted and stacked on a stacking tray, is put to practical use.
An initial sheet processing apparatus having a sheet sorting function has adopted a mechanism in which the stacking tray is moved stepwise toward the width direction in order to shift stacking positions of the sheets toward the width direction. However, it is difficult to move a heavy stacking tray, on which as many as several thousand sheets are stacked, in the width direction from a mechanistic perspective and in view of power consumption. Accordingly, at present, a process tray is arranged on a front stage of the stacking tray, a sheet or a sheet bundle is moved toward the width direction on the process tray, and then the sheet or the sheet bundle is moved and stacked onto an ascendable/descendable stacking tray.
However, the process tray is large in size and constituted of a large number of parts in order to stack the sheets evenly, so the sheet processing apparatus inevitably becomes large in size. In addition, an arrangement place for the process tray is limited to a place immediately before the stacking tray, so it is necessary to arrange the process tray in each branch destination when a sheet conveying path is diverged into a plurality of conveying paths.
Accordingly, proposed is a mechanism in which a pair of rollers arranged on the sheet conveying path are moved toward the width direction while nipping the sheet to thereby shift a sheet conveying position in the width direction of the sheet.
JP S61-33459 A discloses a sheet processing apparatus built in an image forming apparatus. In the sheet processing apparatus, paired discharge rollers for discharging sheets onto a stacking tray are moved in an axial direction to sort and stack the sheets on the stacking tray. The sheets which are obtained after being subjected to image formation and image fixing, and are then discharged onto the stacking tray are moved in two steps toward the axial direction while being nipped by the paired discharge rollers, thereby being sorted and stacked on the stacking tray by shifting the stacking positions of the sheets in the width direction on the stacking tray.
In such the sorting and stacking mechanism disclosed in JP S61-33459 A, the sheets nipped by the paired discharge rollers hang down to the stacking tray, and the nipped sheets are moved in the width direction while causing a friction between the surfaces of a top sheet of the stacked sheets and the nipped sheets. As a result, there is a possibility that a stacked state of the sheets that have been stacked on the stacking tray is disordered.
Therefore, proposed is a technique in which a pair of conveying rollers arranged on an upstream side of the sheet conveying path are moved in the axial direction, and the sheets are moved in the width direction at a position not interfering with the sheets on the stacking tray during the sheet conveyance, thereby discharging the sheets to the paired discharge rollers.
However, it is difficult to secure a linear conveying path having the same length as that of the sheet at a front side of the paired discharge rollers. Accordingly, the sheet is moved in the width direction on a curved conveying path. In this case, there is a possibility that a difference between movement resistances in the width direction is generated between the upstream side of the sheet and the downstream side of the sheet, thereby making the sheet inclined.
The inclination of the sheet which is caused due to a sliding resistance generated between the sheet and a conveying guide is generally called a skew. The skew, generated when the pair of conveying rollers nipping the sheet are moved in the width direction, particularly prominently occurs, in a case of using a sheet having a strong stiffness such as a thick sheet, because the sliding resistance becomes large.
Further, proposed is a technique of achieving a position correcting function in the width direction, in which a position detecting sensor for detecting a position of a side edge of the sheet is combined with the pair of conveying rollers movable in the width direction, thereby aligning the side edges of the respective sheets, or stacking the sheets by aligning each one side edge of the sheets irrespective of using the sheets having different sizes. However, when the sheet itself is inclined through correction of the position of the side edge of the sheet, the side edges of the sheets stacked on the stacking tray are disordered, with the result that the correcting of the position of the side edge of the sheet becomes meaningless.